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I’ve long been suspicious about attempts to see energy as the overwhelmingly central item setting both options and criteria for design in nature. Indeed, when I tried to create a conceptual framework for teaching biology to college students, I ended up putting energy distinctly second to information. Where energy rules, one can find some analog of voltage potential. But in nature, who eats whom boils down to the design and operation of one’s particular teeth and other equipment. I once set up an electrical analog of an ecosystem, but it gave an unreasonable picture until I added ad hoc diodes to keep the trees from eating the caterpillars at night and other such misbehavior. (Steve Vogel, Duke University, 2007)
In materials processing, Nature replaces the massive use of energy (for example high temperatures or harsh chemical reactions) with the use of information (which equates with structure at all levels, molecule to ecosystem). Indeed, most of the exceptional functionality of biological materials is due to their complex structure, driven by their chemical composition and morphology derived from DNA. It is here that the most important aspect of biomimetics emerges, and it has the power to redesign engineering.
There is increasing observational evidence for an implication of the order of interfacial water layers in biology, for instance in processes of cellular recognition and during first contact events, where cells decide to survive or enter apoptosis. Experimental methods that allow access to the order of interfacial water layers are thus crucial in biomedical engineering. In this study, we show that interfacial water structures can be nondestructively analyzed on the nanocrystalline diamond. Results open the gate to a new chapter in the design of biomaterials inspired by biomimetic principles.
Due to their versatility and accuracy, nanoindentation systems are increasingly used for the characterization of micron-sized particles. Single microbial cells (e.g., yeast cells) can be regarded as micron-sized, liquid-filled biological particles. Applying a nanoindentation system for the compressive testing of those cells offers many options, such as testing in liquid environment. However, diverse experimental problems have to be resolved, especially the visualization of the cells in liquid and the alignment of the surfaces between which the cell is compressed. Single yeast cells were tested using a nanoindenter equipped with a flat punch tip. The deformation behavior of the cells during loading as well as the shape recovery behavior during unloading was investigated. A bursting force was determined as the cell wall was failing at higher deformations. Moreover, the influence of the compression speed on the cell mechanical behavior was characterized.
An antigenic mimic of the Ebola glycoprotein was synthesized and tested for its ability to be recognized by an anti-Ebola glycoprotein antibody. Epitope-mapping procedures yielded a suitable epitope that, when presented on the surface of a nanoparticle, forms a structure that is recognized by an antibody specific for the native protein. This mimic-antibody interaction has been quantitated through ELISA and QCM-based methods and yielded an affinity (Kd = 12 × 10−6 M) within two orders of magnitude of the reported affinity of the native Ebola glycoprotein for the same antibody. These results suggest that the rational design approach described herein is a suitable method for the further development of protein-based antigenic mimics with potential applications in vaccine development and sensor technology.
Titania coatings with various morphologies were formed on titanium surfaces by hydrothermal treatment using a dilute alkaline solution and evaluated in their hydroxyapatite (HA)-forming abilities in simulated body fluid (1.5SBF) under ultraviolet (UV) irradiation. The HA formation on the titania coating in 1.5SBF was enhanced by UV irradiation. The amount of phosphate groups adsorbed on the titania, after soaking in 1.5SBF for 24 h under UV irradiation, was estimated to be larger than that of calcium ions, whereas that of calcium ions on the titania, after soaking without UV irradiation, was larger than that of phosphate groups. It was suggested that the titania generated much basic Ti–OH groups at its surface by UV irradiation and subsequently adsorbed phosphate groups, such as H2PO4−, resulting in the formation of a new surface rich in the amount of the groups, which eventually enhanced the HA formation in 1.5SBF.
Apatite films were deposited onto titanium (Ti) metal substrates by an electrodeposition method under a pulse current. Metastable calcium phosphate solution was used as the electrolyte. The ion concentration of the solution was 1.5 times that of human body fluid, but the solution did not contain magnesium ions at 36.5 °C. We used an average current density of 0.01 A/cm2 and current-on time (TON) equal to current-off time (TOFF) of 10 ms, 100 ms, 1 s, and 15 s. The adhesive strength between apatite and Ti substrates were relatively high at TON = TOFF = 10 ms. It is considered that small calcium phosphate (C–P) crystals with low crystallinity were deposited on the Ti surface without reacting with other C–P crystals, H2O, and HCO3− in the surrounding environment. This resulted in relaxation of the lattice mismatch and enhancement of the adhesive strength between the apatite crystals and Ti substrates.
Dental enamel forms through a protein-controlled mineralization and enzymatic degradation process with a nanoscale precision that new engineering technologies may be able to mimic. Recombinant full-length human amelogenin (rH174) and a matrix-metalloprotease (MMP-20) were used in a pH-stat titration system that enabled a continuous supply of calcium and phosphate ions over several days, mimicking the initial stages of matrix processing and crystallization in enamel in vitro. Effects on the self-assembly and crystal growth from a saturated aqueous solution containing 0.4 mg/mL rH174 and MMP-20 with the weight ratio of 1:1000 with respect to rH174 were investigated. A transition from nanospheres to fibrous amelogenin assemblies was facilitated under conditions that involved interaction between rH174 and its proteolytic cleavage products. Despite continuous titration, the levels of calcium exhibited a consistent trend of decreasing, thereby indicating a possible role in protein self-assembly. This study suggests that mimicking enamel formation in vitro requires the synergy between the aspects of matrix self-assembly, proteolysis, and crystallization.
Thermoreversibly gelling block copolymers conjugated to hydroxyapatite-nucleating peptides were used to template the growth of inorganic calcium phosphate in aqueous solutions. Nuclear magnetic resonance (NMR), Fourier transform infrared (FTIR), transmission electron microscopy, x-ray diffraction, and small-angle scattering were used to characterize these samples and confirm that the peptides promoted the growth of hydroxyapatite as the inorganic phase. Three different polymer templates were used with varying charges on the polymer chains (nonionic, anionic, and zwitterionic), to investigate the role of charge on mineralization. All of the polymer-inorganic solutions exhibited thermoreversible gelation above room temperature. Nanocomposite formation was confirmed by solid-state NMR, and several methods identified the inorganic component as hydroxyapatite. Small angle x-ray scattering and electron microscopy showed thin, elongated crystallites. Thermogravimetric analysis showed an inorganic content of 30–45 wt% (based on the mass of the dried gel at ∼200 °C) in the various samples. Our work offers routes for bioinspired bottom-up approaches for the development of novel, self-assembling, injectable nanocomposite biomaterials for potential orthopedic applications.
The mechanical performance of nacre in seashells is generally described in terms of mesoscale mechanisms between mineral plates within the organic polymer matrix. However, recent work has reported nanostructures and organic material within individual plates and associated deformation mechanisms. In this work, we further investigated the nanoscale structure and mechanical behavior within individual plates of nacre by using two methods to induce fracture of plates: microindentation with focused ion beam preparation and ultramicrotomy. Using transmission electron microscopy, we observed deformation nanostructures and organic matrix within plates and identified nanoscale mechanisms, such as separation, shear, and matrix crack bridging.
Implantation of dental and orthopaedic devices is affected by delayed or weak implant-bone integration and inadequate new bone formation. Innovative approaches have been sought to enhance implant-bone interaction to achieve rapid osseointegration. The aim of this study was to develop biomimetic polypeptide nanocoatings and to evaluate cell adhesion, proliferation, morphology, and biocompatibility of polypeptide nanocoatings on implant surfaces. A recently developed nanotechnology, i.e., electrostatic self-assembly, was applied to build polypeptide nanocoatings on implant models, i.e., stainless steel discs. Our in vitro tests using human osteoblast cells revealed that substantially more (one order magnitude higher) osteoblast cells were attached to polypeptide-coated, stainless steel discs than to uncoated discs within the first few hours of contact. The developed biomimetic nanocoatings may have great potential for dental and orthopaedic applications.
Diatoms are well known for the intricately patterned nanostructure of their silica-based cell walls. To date, the optical properties of diatom cell-wall ultrastructures have largely gone uncharacterized experimentally. Here we report the results of a detailed experimental investigation of the way in which light interacts with the ultrastructure of a representative centric diatom species, Coscinodiscus wailesii. Light interaction both with individual valves and whole bivalves of the diatom C. wailesii was measured. Significant sixfold symmetric diffraction through the valve ultrastructure was observed in transmission and quantified to efficiencies that were found to be strongly wavelength dependent; approximately 80% for red, 30% for green, and 20% for blue light. While these results may potentially offer insight into the role of periodic nanostructure in diatom selection, they are also important for consideration in the design of biomimetic optics-based diatom applications.
Biomimetic layer-by-layer (BioLBL) is a layering method in which the binding and mineralization activities of a peptide aptamer are alternately used to accumulate layers of aptamer-displaying nanomaterials and thin mineral strata. We previously demonstrated this in aqua nanofabrication with BioLBL using a recombinant ferritin that displays an aptamer for titanium (minTBP-1) [K. Sano et al.: J. Am. Chem. Soc. 128, 1717 (2006); K. Sano et al.: Nano Lett.7, 3200 (2007)]. To expand the versatility of BioLBL, here we prepared a modified ferritin that was chemically ornamented with minTBP-1 and showed that BioLBL enables the formation of multiple layers of the chemically modified ferritin in a stepwise manner.
Recently, we selected the antibody fragment with high affinity for the biopolymer film of polyhydroxybutyrate (PHB) from human antibody fragment libraries. In this study, we functionalized CdSe quantum dot (QD) nanoparticles by orderly conjugating the anti-PHB antibody fragments to perform spontaneous and selective stacking of inorganic particles on PHB-coated plates in neutral solutions at room temperature. Surface plasmon resonance analysis showed that the orderly clustering of anti-PHB antibody fragment on QD particles led to no dissociation of QD on PHB-coated plates, indicating the availability of avidity effect. The strong spontaneous immobilization using biomolecular recognition enabled stepwise stacking of inorganic particles on PHB-coated plates only by mixing operation in neutral solutions at room temperature. We show the potential of recombinant anti-material antibody fragments for the bottom-up stacking procedures for hybrid assembly.
BioSiC is a biomimetic SiC-based ceramic material fabricated by Si melt infiltration of carbon preforms obtained from wood. The microstructure of bioSiC mimics that of the wood precursor, which can be chosen for tailored properties. When the remaining, unreacted Si is removed, a SiC material with interconnected porosity is obtained. This porous bioSiC is under study for its use as a medical implant material. We have successfully fabricated bioSiC from Sipo wood and studied the kinetics of Si removal by wet etching. The results suggest that the reaction is diffusion-limited, and the etch rate follows a t−0.5 law. The etching rate is found to be anisotropic, which can be explained attending to the anisotropy of the pore distribution. The compressive strength was studied as a function of etching time, and the results show a quadratic dependence with density. In the attainable range of densities, the strength is similar or better than that of human bone.
Diatoms are single-celled algae that make silica shells called frustules that possess periodic structures ordered at the micro- and nanoscale. Nanostructured titanium dioxide (TiO2) was deposited onto the frustule biosilica of the diatom Pinnularia sp. Poly-l-lysine (PLL) conformally adsorbed onto surface of the frustule biosilica. The condensation of soluble Ti-BALDH to TiO2 by PLL-adsorbed diatom biosilica deposited 1.32 ± 0.17 g TiO2/g SiO2 onto the frustule. The periodic pore array of the diatom frustule served as a template for the deposition of the TiO2 nanoparticles, which completely filled the 200-nm frustule pores and also coated the frustule outer surface. Thermal annealing at 680 °C converted the as-deposited TiO2 to its anatase form with an average nanocrystal size of 19 nm, as verified by x-ray diffraction, electron diffraction, and SEM/TEM. This is the first reported study of directing the peptide-mediated deposition of TiO2 into a hierarchical nanostructure using a biologically fabricated template.
Ordered hierarchical mesoporous zirconia fiber was prepared by using collagen fiber as a template, and it was characterized by scanning electron microscopy, transmission electron microscopy, N2 adsorption techniques, x-ray photoelectron spectroscopy, x-ray diffraction, and elemental analysis. It was found that the zirconia fiber obtained is approximately 1–4 μm in outer diameter and 0.5–1 mm in length, and the surface of the fiber exhibits unique corncob-like mesoporous morphology. This study indicates that collagen fiber, with hierarchical supermolecular structures, could be used as an ideal template to prepare porous metal oxide fibers.
We have investigated the polarity of zinc oxide (ZnO) and Al-doped ZnO films grown on (11¯20) and (0001) sapphire substrates, using coaxial impact collision ion scattering spectroscopy. The films grown by pulsed laser deposition with a nominally undoped ZnO ceramic target had a (000¯1) surface, whereas the films prepared with a 1 mol% Al-doped ZnO ceramic target had a (0001) surface. The usage of Al-doped and undoped targets caused no difference in the in-plane lattice orientation. Electron microscope observations revealed that polarity change due to doping occurred without the formation of any interfacial phase between ZnO and sapphire.
It will be shown that in the considered paper, a mistake occurred by handling or editing of experimental data for one of two investigated materials, namely, for cubic germanium nitride having spinel structure (γ-Ge3N4). This mistake led to incorrect values of the shear modulus G0, Young’s modulus E0, and Poisson’s ratio ν0 of this compound. My effort to recover the elastic moduli of γ-Ge3N4 from the available data gave the following results: G0 = 124 GPa, E0 = 326 GPa, and ν0 = 0.32.
The (Ga1−xMnx)N nanorods were grown on Al2O3 (0001) substrates by using rf-associated molecular beam epitaxy. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and selected-area diffraction pattern (SADP) results showed that the (Ga1−xMnx)N nanorods had (0001) preferential orientations. XRD patterns showed that the (Ga1−xMnx)N nanorods contained a small number of grains with different preferred orientations. High-resolution TEM (HRTEM) images showed that the (Ga1−xMnx)N nanorods consisted of different preferentially oriented grains. The initial formation mechanisms for the (Ga1−xMnx)N nanorods grown on Al2O3 (0001) substrates are described on the basis of the XRD, the TEM, the SADP, and the HRTEM results.